The program proposed aims at increasing knowledge about clinical judgment, reasoning, and decision making in relation to the design characteristics for a medical information system oriented to clinical practice. Three of the four subprojects deal with analyzing and optimizing reasoning concerning clinical problems drawn from three specialties--endocrinology, obstetrics/gynecology, and neurology. The fourth subproject concerns development and evaluation of a design theory for practitioner-oriented medical information systems. Information needs identified in the clinical subprojects will be fed into systems design in the informatics subproject. The clinical reasoning subprojects are designed to increase our knowledge of the principles employed by physicians in solving selected clinical problems; to improve our understanding of why competent physicians differ in their judgments of desirable action in a particular clinical problem; to ascertain how much differences in assessments of risks and preferences for different outcomes, rather than knowledge of underlying disease mechanisms, can account for differences in judgments; to determine the clinical findings needed for optimal diagnosis and decision making in selected clinical situations; to develop statistical and probabilistic representations that may have the potential for reducing costs by increasing the efficiency of utilization of low-cost information. The methods of study include retrospective analyses of large numbers of cases using several analytic methods, computer simulations (artificial intelligence), and case vignettes involving clinical decisions. Concepts drawn from research on cognitive processes, problem solving, judgment, policy capturing, and decision making will guide these investigations. A significant aspect of the program is that it deliberately studies, compares, and contrasts the insights into clinical reasoning provided by different models of inference.